1. Field of the Invention
Embodiments of the invention relate to a heated substrate support and method of fabricating the same.
2. Background of Related Art
Thin film transistors (TFTs) are conventionally made on large glass substrates or plates for use in monitors, flat panel displays, solar cells, personal digital assistants (PDAs), cell phones and the like. TFTs are made in a cluster tool by sequential deposition of various films including amorphous silicon, doped and undoped silicon oxides, silicon nitride and the like in vacuum chambers typically disposed around a central transfer chamber. Production of good quality polysilicon precursor films utilized in these structures requires that the hydrogen content of the film be controlled below about 1 percent. In order to achieve this low hydrogen content, post deposition heat treatment of the film at temperatures of about 550 degrees Celsius is required.
As the substrates utilized in TFT manufacture are large, approaching 1.5 square meter in size, preheating the substrates prior to processing is desired to maximize substrate throughput. In order to efficiently preheat the substrates, a preheating chamber is generally coupled to the transfer chamber of the cluster tool that is capable of preheating a plurality of substrates within a vacuum environment. One such preheating chamber is available from AKT, a wholly owned division of Applied Materials, Inc., located in Santa Clara, Calif.
Generally, a substrate is set on one of a plurality of heated substrate supports disposed within the preheating chamber. The substrate support is typically fabricated by vacuum brazing a heating element between two stainless steel plates. The heating element heats the substrate support to a predetermined temperature. The heating element typically comprises a resistive heater disposed on a copper plate. The good heat transfer properties of the copper plate allow the heat from the heating element to be laterally distributed resulting in uniform temperatures across the surface of the shelf supporting the substrate.
Although this conventional configuration of a heated substrate support has shown to be robust and efficient, and produces good temperature uniformity to substrate seated thereon, the vacuum brazing fabrication technique utilized to manufacture the substrate support is expensive and is available only from a limited pool of vendors.
Due to consumer demand and advances in process technology, the size of substrates utilized in the fabrication of LCD's has increased rapidly. For example, substrates over 1 meter in length per side are currently being processed while processing of substrates exceeding 1.5 meter per side is envisioned. Accordingly, the cost of manufacturing substrate supports that can handle substrates of such size utilizing conventional fabrication techniques has increased dramatically with the increase in substrate size and has further limited the pool of vendors capable of producing the substrate supports. Particularly, as substrates approach and exceed 1.2 to 1.5 meters in both length and width, the heated substrate supports fabricated using vacuum brazing techniques are becoming prohibitively expensive.
Therefore, there is a need for an improved substrate support.